1. Field of the Invention
The present invention relates to a ferroelectric material, a ferroelectric thin film, a method of producing a ferroelectric thin film, and a ferroelectric device, in particular, a novel ferroelectric material formed of a lead-free metal oxide.
2. Description of the Related Art
A ferroelectric device is typically formed of a lower electrode and an upper electrode, and a film-shaped ferroelectric material interposed between these electrodes. As a ferroelectric material, lead-type ceramics such as lead zirconate titanate (hereinafter, referred to as “PZT”) is generally used.
However, PZT contains lead as an A-site element, and hence its effect on an environment is considered as a problem. Therefore, a ferroelectric material using a lead-free perovskite-type metal oxide has been proposed.
For example, a ferroelectric material mainly formed of bismuth ferrite, i.e., BiFeO3 (hereinafter referred to as “BFO”) has been proposed as a ferroelectric formed of a lead-free perovskite-type metal oxide.
For example, Japanese Patent Application No. 2007-287739 discloses a BFO-based material containing lanthanum at its A-site. BFO is a good ferroelectric material, and it has been reported that the remanent polarization amount of BFO measured at a low temperature is high. However, BFO involves the following problems. That is, a voltage to be applied to BFO cannot be increased owing to low insulation property of BFO, and BFO is hard to use under a room-temperature environment.
In view of the foregoing, Japanese Patent Application No. 2007-221066 proposes a method of suppressing an increase in leak current, the method involving substituting iron as the B-site element of BFO with manganese to improve the insulation property. However, BFO in which iron atoms are partially substituted by manganese has a problem in that its performance as a ferroelectric is worsened.